Supplementary Information Supramolecular glasses with color-tunable circularly polarized afterglow through evaporation-induced self-assembly of chiral metal–organic complexes

The fabrication of chiral molecules into macroscopic systems has many valuable applications, especially in the fields of optical displays, data encryption, information storage, and so on. Here, we design and prepare a serious of supramolecular glasses (SGs) based on Zn-L-Histidine complexes, via an evaporation-induced self-assembly (EISA) strategy. Metal-ligand interactions between the zinc(II) ion and chiral L-Histidine endow the SGs with interesting circularly polarized afterglow (CPA). Multicolored CPA emissions from blue to red with dissymmetry factor as high as 9.5 × 10−3 and excited-state lifetime up to 356.7 ms are achieved under ambient conditions. Therefore, this work not only communicates the bulk SGs with wide-tunable afterglow and large circular polarization, but also provides an EISA method for the macroscopic self-assembly of chiral metal–organic hybrids toward photonic applications.


Supplementary Note 1: The key to the fabrication of the SGs
In the primary process of the volatilization, the aqueous solution of the metal-ligand complexes was just a free flowing fluid with a low viscosity and consistent structure. However, as the volatilization proceeded, the solution gradually became viscous (as shown by Supplementary Figure 1), just analogous to a supercooled glass-forming liquid 1,2 . It was relatively difficult for the complexes to form crystals in the solution with high viscosity, because the nucleation and crystal growth in these viscous liquids were both mobility-limited 1 . As the free solvent continued evaporating, the more viscous solution "froze" into a glassy state with microscopic inhomogeneity. Hence, we speculate that the key to the fabrication of the supramolecular glass in this work may take the advantage of viscous retardation during nucleation and crystallization upon the evaporation of solution.

Supplementary Note 2: The results of quasi-static compression tests for the SGs
Results of the quasi-static compression tests manifested that the initial yield stress parameters of Zn-L-2 and Zn-L-RB-1/2 SGs were 1.14, 1.00, 0.52 MPa, respectively, which were comparable to that of the 3D-printed sample made from polylactic acid in our daily life 3 , indicating the high stiffness of the glasses 4,5 . The ductile fracture of SGs enabled the supramolecular network structures to be compressed continuously, rather than showed abrupt collapse at a small strain, especially as those of many materials fabricated using crystallization strategy. The decreased compressive strength of the glassy samples by the doping of RB may be caused by the coordination of doped RB to zinc(II) ion 6 , which decreased the network connectivity in the SG matrixes. 99.0%)) in our experiment. The high purity and structure of the commercial L-His were verified by NMR/HR-ESI-MS/FT-IR measurements operated by the manufacturers. In addition, these L-His powders were prepared by using different processes, as well as different animal or non-animal sources. As such, the little residues in these L-His powders may vary in compositions and contents. Significantly, the supramolecular glasses prepared from these L-His powders exhibited almost identical photoluminescence performance (Supplementary Figure 5b), proving that the little residues had negligible effect on structures/properties of the glasses.

Supplementary Note 5: The XPS results for Zn-L glass, crystal and gel
The XPS bands of Zn 2p (binding energies at 1022.0 and 1045.1 eV) and N 1s (binding energy at 399.5 eV) orbitals for Zn-L glass, crystal and gel were nearly identical, implying the similarity of chemical environment and electronic structure of Zn-L complex in the three types of materials 7 . This seemed to further confirm the integrity of the chemical structure of Zn-L complex during volatilization. The bands in N 1s-XPS spectra at 405.9 eV were ascribed to the nitrate ions, which existed as impurities in the glass network. The FT-IR spectra of Zn-L-2/3 and Zn-L-RB-1/2 SGs showed absorption peaks similar to those of Zn-L-1 SG in the range of 4000-400 cm -1 , indicating that there were basically identical coordination structures in these SGs. That is to say, the structural integrity of Zn-L complexes in the glass matrix could be confirmed during the volatilization process and even doped with RB. Considering that, the very close CD, 1 H NMR, and FT-IR spectra between the SGs and the single crystal form confirmed the structure of Zn-L complex in the SG was highly similar to that in the crystalline state ( for Zn-L-1 SG, while the overall weight losses in the range of 25-130 °C were 3%, 5.3% for Zn-L-2/3 SGs, respectively. The initial degradation temperature of Zn-L-3 SG was below 225 °C and its specific value could not be determined by the curve.
In the TGA trace of Zn-L-1 SG, the continuous weight loss in the range of 25-150 °C was mainly related with the gradual loss of free water molecules and hydrogen-bonded water molecules. In contrast, the almost complete loss of the structured water occurred at 130 °C for Zn-L-2 SG. These reflected that there existed stronger hydrogen-bonding between solvent water molecule and the complex in Zn-L-1 SG compared to that in Zn-L-2 SG. Notably, as the volatilization proceeded, for Zn-L-3/2/1 SGs, relatively more structured water molecules and a smaller proportion of free water molecules existed in the glass matrix, which resulted in an increase of the network connectivity in light of lowering of the probability for free water molecules to intervene in the connection between the neighbored supramolecular structural units. Moreover, Zn-L-1/2 SGs showed the initial degradation temperatures at approximately 233 and 225 °C, respectively, which were higher than that of Zn-L-3 SG. Based on these results, the phenomenon that the initial degradation temperature increased with the increase of solute mass fraction in Zn-L-1/2/3 SGs indicated that the enhanced non-bonded interactions were conducive to the construction of a highly stable polymeric structure.
The initial degradation temperature of Zn-L-2 SG was higher than those of the dye doped samples (Zn- Figure 11b), probably because the coordination between trace RB and Zn 2+ was not conducive to the structurally thermal stability of the SGs 6 .
In the wavelength range of 200-1800 nm, the as-synthesized glasses showed several absorption bands, which were attributed to Zn-L complexes (cyan areas), RB (pink area) and water (blue areas), respectively.   Figure 23b). These results corroborated the successful achievement of PRET from the Zn-L complexes to the dyes, benefiting from the large overlap between the RTP spectrum of Zn-L complexes and the absorption spectrum of the dyes molecules as well 16,17 . Hence, it was reasonable to conclude that the large spectral overlap was a prerequisite for the PRET process.

Supplementary Note 16: The luminous behaviors of Zn-L crystal
The prompt PL spectrum of Zn-L crystal exhibited a sharp peak in the ultraviolet region (λem = 360 nm) and one shoulder peak in the range of 440-600 nm (Supplementary Figure 26a). Its delayed PL spectrum (λem = 509 nm) nearly overlapped with the region of the shoulder peak in the prompt one, manifesting that the luminescence of Zn-L crystal featured both blue fluorescence and green phosphorescence characteristics.

Supplementary Note 17: The analyses about the glum achieved in the SGs
Theoretically, glum can be calculated according to the equation: glum = 4(|u||m|cosθμ,m)/(|u| 2 +|m| 2 ) 18,19 , where u and m represent the electric and magnetic transition dipole moments, respectively, and θμ,m represents the angle between these two dipole moments. |glum| reaches the maximum value of 2 when u and m are equal to each other in length and oriented in either the parallel or antiparallel direction. However, due to fact that the length of m is generally much smaller than that of u in most of small organic molecules, the denominator in the equation is dominated by |u| 2 , which generates the simplified equation: glum ≈ 4|m|cosθμ,m/|u|. Hence, larger dissymmetry factor can be obtained through electrically forbidden (i.e., small |μ|) and magnetically allowed (i.e., large |m|) transitions, such as the (n, π*) characteristic in carbonyls 19 . In view of factors above, the large luminescence dissymmetry factors achieved in the SGs could be largely attributed to the macroscopic selfassembly of Zn-L complexes, as well as the efficient (n, π*) state involved transition facilitated by the nitrogen and oxygen atoms.  Remarkably, a series of measurements have also yielded strong evidence for the proposed PRET mechanism.
The strong RTP emission with high air stability (even after 5 months) of Zn-L-2 SG indicated a strong oscillator strength of the T1→S0 transition (Supplementary Figure 35c) 20 . It was speculated that the stable phosphorescence may benefit from strong SOC with the contribution of (n, π*) states facilitated by nitrogen/oxygen heteroatoms. The strong SOC and consequent efficient RTP were crucially important, because the oscillator strength of phosphorescence in the donor served as a precondition for the dipole-dipole coupling between the excited donor and ground-state acceptor to promote the PRET process.
Time-resolved emission decay profiles of Zn-L-2 and Zn-L-RB-1/2 SGs showed the gradual decrease of the lifetime from 307.9, 176.3, to 141.9 ms upon increasing the RB-doping ratio from Zn-L-2, Zn-L-RB-1, to Zn-L-RB-2 SGs (Fig. 4), which hinted the non-existence of emission-reabsorption process and further supported the concept of PRET 21 .  The m stands for the double-or three-exponential fitting of the PL decay curve, the τi represents the excited state lifetime, the Ai represents the ratio of τi, the value of χ 2 manifests the goodness of fitting, which is required to be below 1.300.

Supplementary Note 21: The results of TD-DFT calculations for L-His and Zn-L monomers
As we have known, the possible ISC process needs to follow at least two factors based on the energy gap law:  Table   3, 4), for Zn-L monomer, the transition configurations of the three excited triplet (T1-T3) were all contained in the transition configurations of the S1, which greatly facilitated the transition of excitons from singlet to triplet states. However, for L-His monomer, although it exhibited six excited triplet states between ES1 ± 0.4 eV, a very small proportion of the transition configurations of the T1-T6 were obtained in the transition configurations of the S1. According to the theoretical and experimental results, it was deduced that there existed a higher probability of ISC progress in Zn-L monomer compared with that in L-His monomer, although the total number of plausible ISC channels in L-His monomer was more than that in Zn-L monomer.